A survey of more than 25 million galaxies has found a surprising discrepancy in how astronomers measure the collapse of the universe, and it could threaten the standard model of cosmology, which describes how the universe formed. and the universe evolved.
The difference, found by measuring the warping of light by the powerful gravitational fields of distant galaxies, suggests that the cosmos is less packed-together than previously predicted.
If the measurement is accurate, it will join the Hubble tension as another significant challenge to our preconceptions of how the cosmos evolved – one that could lead to new physics or even a different model of the universe. The researchers published their findings on December 11 in the journal Physical Review D.
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“We’re still being careful here,” Michael Strausschair of Princeton University’s Department of Astrophysical Sciences and one of the leaders of the team that made the discovery, said in a statement. “We are not saying that we have just discovered that modern cosmology is all wrong. Statistics show that there is only one in 20 times that it is due to chance, which is compelling but not completely definitive. But as we in The astronomical community have the same conclusion with many experiments, as we continue to make these measurements, we may know that it is true.”
According to the standard model of cosmology, after the Big Bang the young cosmos is a moving plasma soup that begins to rapidly expand due to an invisible force known as dark energy. As the universe grew, ordinary matter, interacting with light, was filled with clusters of the invisible. black matter to create the first galaxies, connected together in a vast cosmic web. Today, cosmologists think that ordinary matter, dark matter and dark energy make up about 5%, 25% and 70% of the universe, respectively.
Yet there are growing problems with this picture. To test their models, astronomers often compare the past to the present universe. Their previous measurements were taken from the cosmic microwave background (CMB), the static fizz of the universe’s first light that left its source (recombining atoms) 380,000 years after the Big Bang.
But the Hubble constant – a value that tracks the rate of expansion of the universe – predicted from the CMB does not agree with calculations obtained from celestial objects in the contemporary cosmos. This discrepancy led to a cosmological crisis known as the Hubble tension.
The new distinction about the lumpiness of the universe centers on a number called S8, which measures how many objects are clusters, or clumps together, throughout the universe. After using the Planck satellite to study the cosmic microwave background (CMB), astronomers then plugged the data into the standard model of cosmology and obtained a predicted value for S8 of 0.83.
This is matched by a new measurement of S8 using the Subaru Telescope in Japan, which studies how much light is refracted by the presence of matter in galaxies. The researchers took these results and produced a smaller value for S8 of 0.77. The new result is replicated by two other collaborations that map matter in the universe using gravitational lensing – the Dark Energy Survey and the Kilo-Degree Survey – making individual anomalous results impossible.
“We confirm the growing community feeling that there is a real difference between the clumping measurement of the early universe (measured from the CMB) and that from the time of galaxies, ‘only’ 9 billion years ago, ” Arun Kannawadi, an associate research scholar at Princeton University who was involved in the analysis, said in the statement.
Although the problem points to another huge hole in our understanding of the universe, cosmologists don’t yet have good ways to fill it. It’s possible that cosmologists are wrong about the amount of dark matter in the universe, or how it clumps together. Perhaps dark energy has changed over the course of the universe’s life — an explanation that could resolve the tension between S8 and Hubble with a tweak to the standard model of cosmology.
Or perhaps, most exciting of all, it may mean that the standard model is broken and requires a total replacement. In order for scientists to know for sure, they will make more accurate measurements from more powerful telescopes. Two of those contenders are the Vera C. Rubin Observatory in Chile and the Nancy Grace Roman Space Telescope, which will come online in 2025 and 2027, respectively.
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